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                <i class="fas fa-angle-double-right"></i>Python常用方法
            
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            <h1 id="python-常用方法"><a href="#python-常用方法" class="headerlink" title="python 常用方法"></a>python 常用方法</h1><h2 id="保留小数"><a href="#保留小数" class="headerlink" title="保留小数"></a>保留小数</h2><p>使用字符串格式化</p>
<pre><code class="python">a = 11.234
print(&quot;%.2f&quot;%a) </code></pre>
<p>使用round内置函数</p>
<pre><code class="python">a = 11.234
a = round(a,2)
print(a) </code></pre>
<p>使用decimal模块</p>
<pre><code class="python">from decimal import Decimal
a = 12.345
Decimal(a).quantize(Decimal(&quot;0.00&quot;)) </code></pre>
<h2 id="列表"><a href="#列表" class="headerlink" title="列表"></a>列表</h2><h3 id="列表合并"><a href="#列表合并" class="headerlink" title="列表合并"></a>列表合并</h3><pre><code class="python"># 使用+号操作
list1 = [1,2,3,4,5]
list2 = [&quot;z&quot;,&quot;xx&quot;,] 
list3 = list1+list2
# 使用extend
list4.extend(list1)
# 使用切片
list4[len(11):len(11)] = list5</code></pre>
<h2 id="os模块"><a href="#os模块" class="headerlink" title="os模块"></a>os模块</h2><h3 id="Python获取指定文件夹下的文件名"><a href="#Python获取指定文件夹下的文件名" class="headerlink" title="Python获取指定文件夹下的文件名"></a>Python获取指定文件夹下的文件名</h3><p><font color='red'>模块os.walk可以遍历文件夹下的所有文件</font></p>
<pre><code class="python">os.walk(top, topdown=Ture, οnerrοr=None, followlinks=False)
# return  (dirpath dirnames filenames)</code></pre>
<ul>
<li>dirpath: string 代表目录的路径</li>
<li>dirnames list 包含了当前dirpath路径下所有的子目录名字（不包含目录路径）</li>
<li>filenames：list，包含了当前dirpath路径下所有的非目录子文件的名字（不包含目录路径）。<pre><code class="python">import os
</code></pre>
</li>
</ul>
<p>def file_name(file_dir):<br>    for root, dirs, files in os.walk(file_dir):<br>        print(root) #当前目录路径<br>        print(dirs) #当前路径下所有子目录<br>        print(files) #当前路径下所有非目录子文件<br>        for file in files:<br>            # os.path.splitext # 对文件名进行切割成数组<br>            if os.path.splitext(file)[1] == “.jpeg”:<br>              print(file)<br>            else:<br>              pass</p>
<pre><code>
&lt;font color=&#39;red&#39;&gt;模块os.listdir()可以得到当前路径下的文件名，不包括子目录中的文件&lt;/font&gt;

```python
import os
# 遍历获取所有文件
def listdir(path, list_name):
    for file in os.listdir(path):
        file_path = os.path.join(path, file)
        # os.path.isdir(file) #判断文件是否为文件夹
        if os.path.isdir(file_path):
            listdir(file_path, list_name)
        elif os.path.splitext(file_path)[1]==&#39;.jpeg&#39;:
            list_name.append(file_path)</code></pre><h3 id="判断文件类型"><a href="#判断文件类型" class="headerlink" title="判断文件类型"></a>判断文件类型</h3><pre><code class="python">os.path.isdir(path) # 是否为文件夹
os.path.isfile(path) # 是否为文件</code></pre>
<h2 id="文件操作"><a href="#文件操作" class="headerlink" title="文件操作"></a>文件操作</h2><p>mode选项<br>r 读模式，只能读 文件不存在报错，<br>w 写模式，只能写 文件不存在则创建，<br>以上存在存在则清空在打开</p>
<p>rb 二进制读模式 只能读  文件不存在报错<br>wb 二进制写模式 只能写  文件不存在则创建，<br>以上存在则清空再打开<br>有二进制内容 写入则需要encode(“utf-8”)</p>
<p>rb+ 二进制读模式 可读可写 文件不存在报错<br>wb+ 二进制写模式 可读可写 文件不存在则创建，<br>以上存在则清空再打开</p>
<p>a 追加写模式，文件存在则追加写入<br>a+ 追加读写方式<br>以上存在则追加写入</p>
<p>默认进入为文件末尾<br>f.seek(0) 设置读写位置为开头<br>f.truncate(0) 将文章字节阶段为0</p>
<h3 id="文件头部写如文件"><a href="#文件头部写如文件" class="headerlink" title="文件头部写如文件"></a>文件头部写如文件</h3><pre><code class="bash">with open(path, &quot;r+&quot;) as f:
     old = f.read()
     f.seek(0)
     f.write(data)
     f.write(old)</code></pre>
<p>或者</p>
<pre><code class="bash">with open(path,&quot;a&quot;) as f:
      f.seek(0)
      old = f.read()
      # 全部删除
      f.truncate(0)
      f.write(&quot;---&quot;)
      f.write(&quot;tags: xxx&quot;)
      f.write(&quot;---&quot;)
      f.close()</code></pre>
<h2 id="python应"><a href="#python应" class="headerlink" title="python应"></a>python应</h2>
        </div>
        
            <ul class="post-copyright">
            <li><strong>本文标题：</strong><a href="http://alpaca-h.gitee.io/2019/12/27/blog_back_new/Python/python%E5%B8%B8%E7%94%A8%E6%96%B9%E6%B3%951/">Python常用方法</a></li>
            <li><strong>本文作者：</strong><a href="http://alpaca-h.gitee.io">Alpaca</a></li>
            <li><strong>本文链接：</strong><a href="http://alpaca-h.gitee.io/2019/12/27/blog_back_new/Python/python%E5%B8%B8%E7%94%A8%E6%96%B9%E6%B3%951/">http://alpaca-h.gitee.io/2019/12/27/blog_back_new/Python/python%E5%B8%B8%E7%94%A8%E6%96%B9%E6%B3%951/</a></li>
            <li><strong>发布时间：</strong>2019-12-27</li>
            <li><strong>版权声明：</strong>本博客所有文章除特别声明外，均采用 <a href="https://creativecommons.org/licenses/by-nc-sa/4.0/deed.zh" rel="external nofollow" target="_blank">CC BY-NC-SA 4.0</a> 许可协议。转载请注明出处！
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